Adults with PKU and brain damage : Composition and management of a protein restricted diet

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Abstract

Summary

Phenylketonuria (PKU) is an inborn error of metabolism, due to a defective liver enzyme the conversion of the amino acid phenylalanine (phe) to tyrosine is not functioning. PKU was first described in 1934 by the Norwegian doctor and scientist Asbjørn Følling. Without treatment persons with PKU suffer permanent neurological damage and mental retardation. Today newborn screening programmes result in early diagnosis. Dietary treatment is started shortly after birth to prevent brain damage. The intake of phe is restricted by allowing only small amounts of protein in the diet. Requirements are met by taking a protein substitute containing amino acids, vitamins and minerals. Special low protein food secure energy requirement. For a person with brain damage due to late diagnosed PKU, dietary treatment may ease neurological and behavioural signs. Positive effects are reported for a majority of late diagnosed patients after treatment start. Literature on how these persons and their caregivers translate the advice and prescriptions from doctors and dietitians into an everyday diet is lacking.

The objective of the present study was to analyse the composition of dietary intake and describe how adults with PKU and brain damage manage the diet.

Methods:

An observational cross-sectional study was performed on 21 subjects with brain damage and adhering to a PKU diet: 8 men, 13 women; 26 – 66 years of age. Seven mildly retarded subjects living independently constituted group A. Group B consisted of fourteen severely retarded subjects needing continuous support and living in group homes. Data were collected by a four-day weighed food registration, a semistructured interview, blood samples and hospital charts. Descriptive statistics were used in analysing.

Results:

Serum phe was lowered by the diet to a median 472µmol/L. Median intake of selected nutrient: 1.02 g/kg protein (substitute and natural protein), 26 E% from fat, 15 E% from added sugar and 1.7 g/MJ of dietary fibre. The median intake of fruit and vegetables was 370g/d, comparable to the Norwegian mean intake. Fortification resulted in excessive intakes of micronutrients and high blood concentrations of folate and vitamin B12. Other blood parameters as iron, zinc or magnesium, did not show the same effect despite high intakes. The intake was above estimated upper limit for a few nutrients, as iron.

Discussion and conclusion:

The study showed that adults with PKU and brain damage could manage a diet according to nutritional recommendations. However, this required great efforts and special considerations regarding food choice. The fortification of micronutrients is excessive and the doses and compounds used need evaluation in order to compose an optimal diet. The subjects in group A faced great challenges in adhering to the diet. Practical support was needed to maintain low serum phe levels and compose a varied diet. Managing the diet in group B depended on mutual agreement and a basic knowledge of PKU among the group home staff, this improved cooperation and supported the responsible caregivers. Caregivers in group B requested information and knowledge, whereas the psychological and emotional aspects of adhering were more important for subjects in group A.

This study has provided new knowledge that can prove important in regard to giving dietary advice and in organising follow-up of persons with PKU and brain damage. It may also stimulate an improved cooperation between local and central systems for treatment and support. The results of the present study also show that further investigation into the nutritional impact of a semi-synthetic diet is required.